1. Field of the Invention
The present invention relates to a composite-plated article in which a composite-plating film comprising nickel or a nickel alloy compounded with a carbon nanocomposite fiber covers a metallic material, and to a method for producing the same.
2. Background Information
Nickel plating treatments have long been used in order to protect the surface of metallic materials and improve their design. In recent years, ultrafine carbon nanofibers have been brought into commercial use, and a variety of proposals have been made for applications concentrating on their strength, thermal conductivity, and electroconductivity. Among these proposals, a technique is known for mixing carbon nanofibers in a nickel-plating bath and performing composite plating as disclosed in, e.g., JP 2001-283716 A. The composite-plating technique disclosed in JP 2001-283716 A will be described next with reference to FIG. 7 hereof.
FIG. 7 shows a nickel plating film 102 with fullerenes 101 dispersed therein, the film being obtained by blending the fullerenes into a nickel plating bath, and performing an electric (electrolytic) plating treatment.
After having inspected the resulting film, the present inventors discovered that the strength of the nickel plating film 102 had not increased to the expected degree. They accordingly examined the nickel plating film 102 under a microscope, which revealed very fine gaps between the fullerenes 101 and the nickel plating film 102. If the fullerenes 101 move about within the nickel plating film 102, their reinforcing effect declines, and any increase in strength is minimized as a result. Accordingly, there is a demand for a composite-plating technique that receives the strengthening effect of the carbon nanofibers, while presenting no concerns regarding decreased strength.
The present inventors have previously proposed a method for adding carbon nanofibers to a Watts bath and obtaining a composite-plating film to improve surface roughness, as is disclosed in JP 2006-028636 A.
In JP 2006-028636 A there is disclosed a method for producing a fiber-shaped nanocarbon/metallic composite material, the method characterized in that a brightening agent, polyacrylic acid, and carbon nanofibers are mixed into a Watts bath containing mainly nickel sulfate and nickel chloride so that a composite-plating solution is obtained; a metallic material is introduced into the plating solution; and an electrolytic plating treatment is performed, whereby a composite-plating film in which a fibriform carbon nanomaterial is compounded with nickel attaches to the metallic material. According to this method, the brightening agent and the polyacrylic acid serve to produce a smoother plating film.
However, since carbon nanofibers are highly electroconductive, electrolytic plating will cause the plating film to form on surfaces of the carbon nanofibers. As a result, the smoothing effect obtained by the brightening agent and the polyacrylic acid is limited and inadequate, necessitating further smoothing to be performed.